Admittedly I was thinking along the lines of gin and other drinks herbal contents. But while Buckfast Abbey is guarded about "the recipe" they say it is essentially the same as it was 120 years ago. It is said to be made from "fortified wine" (which besides alcohol and sugar, is loaded with plant based tannins, some reservatrol, and any number of extra ingredients), a couple of preservatives, vanilla extract... and it has caffeine in it.

It seems like a liability for the traditional branding if they do not make it as they claim "along the same lines and according to the same basic recipe as used in the very early days" They could be just mixing in highly refined caffeine like an "alcho-pop" manufacturer but I'm not so cynical to expect that.